In the polyurethane field, increased interest is being shown in compounds which can be added to the polyurethane polymers to act as flame retardant agents. Particular interest is being shown in compounds which have functional groups reactive with the polyol or polyisocyanate used in preparing the polyurethane so that the flame retardant agent can be copolymerized into the polymer chain. One such group of reactive flame retardants are the polyalkylene glycol phosphites such as those described in U.S. Pat. No. 3,009,939. However, these materials, due to their high OH number and crosslinking tendency, are unsuitable for use in flexible urethane foams. In U.S. Pat. Nos. 3,081,331 and 3,142,651, there is disclosed a method of forming polyalkylene glycol polyphosphites having up to 10 phosphite groups in the polymer chain by reacting a trialkyl phosphite with a polypropylene glycol in a molar ratio of 2.1 to 2.5 moles of glycol per mole of phosphite. These materials are also unsuitable for use in flexible urethane foams as a result of their high OH numbers and their tendency to crosslink.
Another attempt at employing reactive flame retardants, described in U.S. Pat. Nos. 3,142,651 and 3,092,651, involves the use of polypropylene glycol poly-hydrogenphosphonates produced by a thermal polymerization. Likewise, polyalkylene glycol hydrogen polyphosphonates have also been produced by transesterifying a secondary hydrogen phosphonate with a polyalkylene glycol according to the procedure outlined in British Pat. Nos. 796,446 and 1,011,118. However, many of these materials have relatively high acidity, causing them to react with and thereby deactivate the catalyst systems generally used in the formation of polyurethane polymers such as, for example, tertiary amine compounds. The former method has the additional drawback of contamination of the product by the alkylene glycol by-product, which contaminant is not easily removed.
In order to increase the flame retardancy of some of the above described phosphorus compounds, which have low phosphorus content, the prior art has attempted to incorporate various halogen containing substituents into the above described molecules. Thus, U.S. Pat. Nos. 3,159,605 and 3,167,575, describe the reaction of halogenated methanes with these compounds. Likewise, U.S. Pat. Nos. 3,131,206 and 3,328,493, describe the reaction of chloral with them. However, these materials, like their precursors, have many drawbacks. In particular, these products have high OH numbers and low phosphorus content thereby rendering them less suitable as flame retardants in flexible urethane foams.
In addition to these above-mentioned prior art references, Review In Marcomolecular Chemistry, Vol. II, N.Y.C. 1967, discloses that polyalkylene glycol alkyl phosphonates have been prepared by reacting an alkyl phosphonic acid dichloride with a polyalkylene glycol. This procedure was originally reported by Korshak et al, in Vzsokomolekuylarnye Soedineniya 2, 427-32 (1960). In a subsequent article by Tormosina et al, Khim. Khim. Tekhonol. 1968, 31-41, the polyalkylene glycol alkyl phosphonates prepared by this route are disclosed as containing unhydrolyzed chlorine and being too acidic for use in polyurethane foam. Furthermore, Korshak et al, Izv. Akad. Nauk. SSSR, Otd. Khim. Nauk. 1963(6), 1095-1100, disclose the preparation of polyalkylene glycol alkyl phosphonates by transesterifying dimethylmethylphosphonate with diethylene glycol. The product, however, is disclosed as being characterized with an acid number of from 240 to 400 mg. of KOH/gm. of sample and accordingly is also unsuitable for use in polyurethane foam.
In U.S. Pat. Nos. 3,798,290, and 3,819,750, there are disclosed novel polyalkylene glycol vinyl phosphates and novel mixed polyalkylene glycol vinyl phosphates and phosphites which are prepared by reacting a halogenated carbonyl compound with a polyalkylene glycol alkyl polyphosphite. While these vinyl phosphonates yield polyurethane foam having excellent flame retardant and physical characteristics, they have recently been found to impart a slight odor to the foam which may be considered objectionable.